Storage system which utilizes two kinds of memory devices as its cache memory and method of controlling the storage system

Abstract

Provide is a storage system including one or more disk drives, and one or more cache memories for temporarily storing data read from the disk drives or data to be written to the disk drives, in which: the cache memories includes volatile first memories and non-volatile second memories; and the storage system receives a data write request, stores the requested data in the volatile first memories, selects one of memory areas of the volatile first memories if a total capacity of free memory areas contained in the volatile first memories is less than a predetermined threshold, write data stored in the selected memory area in the non-volatile second memories, and changes the selected memory area to a free memory area. Accordingly, there can be realized capacity enlarging of the cache memory using a non-volatile memory device while realizing a high speed similar to that of a volatile memory device.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]The present application is a continuation of application Ser. No. 13 / 206,838, filed August 10, 2011; which is a continuation of application Ser. No. 12 / 106,607, filed Apr. 21, 2008; which claims priority from Japanese application JP2008-45731 filed on Feb. 27, 2008, the content of which is hereby incorporated by reference into this application.BACKGROUND OF THE INVENTION[0002]A technology disclosed herein relates to a storage system including a cache memory, and more particularly, to a storage system including two kinds of cache memories, that is, volatile and non-volatile cache memories.[0003]Conventionally, a storage system including hard disk drives has been provided with a cache memory which temporarily stores data read or written by a host computer, thereby increasing speeds of reading and wring data. As a memory device used for the cache memory, conventionally, a dynamic random access memory (DRAM), which is volatile but is much fas...

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Benefits of technology

[0006]This invention has been made in view of the above problems. An object of this invention is, for sufficient effect of a cache memory of a storage system, to realize capacity enlarging using non-volatile memory devices such as a flash memory while realizing a high speed similar to that of volatile memory devices such as a DRAM. Another object of this invention is to decrease the capacity of batteries provided for a power down compared with a configuration which enlarges the capacity of only volatile memory devices such as the DRAM.

[0008]It is possible to enlarge the capacity of a cache memory of a storage system while keeping the read and write speeds. Moreover, it is possible to decrease the size, weight, and power consumption of a system by decreasing the capacity of batteries provided for a power down.

Problems solved by technology

Therefore, the throughput of the write as the system is limited to a low write speed of the non-volatile memory device.

Moreover, the non-volatile memory device is inferior in read speed to the volatile memory device such as the DRAM, which less contributes to an increase in the speed of the data read.

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